Torque sensors are applied broadly in the field of engineering industry, such as for example torque sensors used in an electric power assisted steering system of an automobile. Torque sensors may be based on a resistance potentiometer, in which a conventional torque sensor is in the form of a potentiometer. A mechanical contact is established and the contact position of the potentiometer changes. Since the potentiometer and a circular ring rub are continually in contact with the fixed wall, the frequent rotation of the potentiometer and the circular ring will render abrasion, which greatly reduces the life of the sensor. At the same time, because of the frictional resistance, performance may be poor during operation of the steer device. At the same time, the sensing precision of the sensor to the torque of the steer device will also be reduced. Furthermore, as to the conventional potentiometer torque sensors, the transition process from torque to an electric signal includes a lot of intermediate links and also involves quite a great number of components, which results in high costs.
Furthermore, a grating torque sensor is known, which measures a torsion angle by the relative displacement of the grating and then converts the change of a light beam into an electric signal and outputs a corresponding torque signal after amplification and corresponding processing by a circuit. The grating torque sensor is not subject to the problem of abrasion and has a longer life and a high precision as it is non-contact, however the manufacturing costs are quite high and the grating requires a high precision. Also the manufacturing process is more complicated, thus, the grating torque sensor is seldom adopted in a general electric power assisted steering system.
A further type of torque sensor uses a magnetic detection to detect a change of the position. It would be beneficial to have a torque sensor based on magnetic field detection with a simple structure, simple manufacturing process, and high precision.